MOSCOW (Reuters) - When Ahn Hyun-soo switched allegiance from South Korea to Russia for the Sochi Winter Games, he took the name Viktor for good luck.

Two years ago, the 28-year-old short-track skater took on Russian citizenship and became Viktor Ahn when he fell out with the South Korean speed skating federation after failing to win a spot for the 2010 Olympics in Vancouver.

He now trains full-time at a sports complex outside Moscow, preparing for a comeback at the Sochi Games in his adopted homeland - pushing himself to return to top form after a knee injury in 2008 nearly crippled his career.

Going into Sochi, the five-time overall world champion from 2003 to 2007 said he now feels nervous and excited, much as he did at the start of his career.

"The strange thing about this Games is that I have a feeling of preparing for it as if for my first competition so I am trying to regain all of my strength to focus on this goal," Ahn, who is grappling with the Russian language, told Reuters through a translator after a 90-minute morning practice at his new rink.

In 2006 at Turin, Ahn became the first ever short track speed skater to win four Olympic medals at a single games - gold in the 1,000 meters, 1,500m and 5,000m relay and bronze in the 500m.

But a violent crash during training in 2008 ended his winning streak, fracturing his knee and putting him out of competition for over a year.

"A lot of time has passed since the first Olympic Games I took part in, and I didn't know if I had enough strength to pursue this goal again," said Ahn, who packs sprinting power into a slight build.

"I was nervous and it is exciting for me to return to such a big competition."

Despite four surgeries, Ahn said he has adjusted to feeling twinges of pain during practice.

Fame In His New Homeland

Although Russia has long been a winter sports powerhouse, the only medal it has won in short track was a bronze at Albertville in 1992, when competing as the Unified Team. South Korea has long been the dominant nation, winning 19 golds, 12 more than any other nation.

Ahn's defection is a chance for Russia to turn that record on its head. The experience he has brought to Russia has helped improve the competitiveness of the entire team.

Ahn said his new Russian name was inspired in part by the legendary Soviet rock singer Viktor Tsoy. "I want to become famous in Russia like Viktor Tsoy," he said. The lead singer of the iconic Kino band of Korean descent.

The short-track star, who had complained of a lack of support from the South Korean speed skating federation, said he is happier, having left behind the rivalries in his birthland, and hoping to give something back to his adopted country.

"There was a situation that prevented me from training comfortably in South Korea, but in Russia, the sports atmosphere is great, it's amazing," said Ahn.

"I am more comfortable, more relaxed here."

Russia is sending a maximum quota of three skaters for each short track event in Sochi thanks to a strong season by Ahn and his teammate Vladimir Grigorev.

Ahn has shown he is in good form with two confidence-boosting World Cup wins in the 500m this season but faces steep competition from Canada's Charles Hamelin, the 2010 Olympic champion in the 500m and current leader of the overall rankings.

"Short track is about competing with other sportsmen and less about speed ... the approach to my competitors can be different in each situation," Ahn said.

"I concentrate on my own skills and preparation to try to win naturally.

"My strategy will have many changes since the previous Olympics (in 2006) since the sport itself has evolved."